The present invention relates generally to a vehicular transmission system utilizing a centrifugal master friction clutch. In particular, the present invention relates to an automated vehicular transmission system comprising an engine, a multiple ratio transmission, a centrifugally operated master friction clutch for drivingly coupling the engine to a transmission and a control unit for controlling fueling of the engine during prolonged operation of the centrifugal clutch in a partially engaged condition.
Automated mechanical transmission systems not requiring the vehicle driver or operator to operate the vehicle master clutch (so called xe2x80x9ctwo-pedal systemsxe2x80x9d) are known in the prior art, as may be seen by reference to U.S. Pat. Nos. 4,081,065; 4,361,060, 4,936,428; 5,439,428; 5,634,867; 5,630,773; 5,960,916; and 5,947,847, the disclosures of which are incorporated herein by reference in their entirety. These systems are not totally satisfactory as separate clutch actuators, sensors and/or, electrical and/or fluid power (i.e., compressed air and/or hydraulic) connections thereto are required which adds to the expense of assembling and maintaining such systems.
Centrifugally operated friction clutches are well known in the prior art and typically include an input member driven by a primer mover, usually an electric motor or internal combustion engine, and weights pivotable or rotatable with respect to the driving member which, upon rotation of the input member, will move radially outwardly under the effect of centrifugal force to cause the input member to frictionally engage an output member. Examples of centrifugally operated clutches may be seen by reference to U.S. Pat. Nos. 3,580,372; 3,580,372; 3,696,901; 5,437,356; 3,810,533; 4,819,779; 5,441,137; 5,730,269; and 4,610,343, the disclosures of which are incorporated herein by reference in their entirety.
Vehicular transmission systems, especially for heavy-duty vehicles, utilizing centrifugal clutches permit a driver to hold the vehicle on a grade or encourage the vehicle to xe2x80x9ccreepxe2x80x9d by increasing the speed of the engine to a point sufficient to partially engage the clutch. A drawback of this approach is that partially engaging the clutch for an extended period of time expedites wear of the friction materials and causes the clutch to develop a large amount of heat, both of which contribute to a reduction in the operative life of the clutch.
A vehicular transmission system utilizing a centrifugal master clutch is disclosed in a pending U.S. patent application Ser. No. 09/814,494, filed Mar. 21, 2001, which is owned by the assignee of the present invention and is hereby incorporated by reference in its entirety. This reference discloses a control system and method of providing damage and/or overheating protection for a centrifugal clutch. Upon sensing a potential overheating problem, the control system reacts by increasing or decreasing the speed of the engine. If the engine speed is increased, the clutch will fully engage causing the driver to use a different method of maintaining the vehicle position. If the engine speed is decreased, the clutch will disengage requiring the driver to increase the throttle position to engage the clutch. While this method has proven to be effective in preventing damage and/or overheating of the clutch, the automatic engagement or disengagement of the clutch is undesirable for a driver.
In accordance with an embodiment of the present invention, a control system and method of controlling a vehicular automated transmission system utilizing a centrifugal master friction clutch is provided. The inventive control system and method utilizes closed loop control to provide the clutch with protection from damage and/or overheating due to the clutch being operated in a partially engaged state.
In a preferred embodiment, a vehicular automated transmission system is provided that includes an internal combustion engine having a flywheel, a multiple speed transmission having an input shaft and a centrifugal friction clutch drivingly connecting the engine flywheel to the input shaft. An engine controller having at least one mode of operation is utilized for controlling engine fueling to control at least the engine speed. The transmission system further includes a control unit for receiving input signals indicative of various vehicle operating conditions and processing the signals according to logic rules to issue command output signals to system actuators including at least the engine controller.
The inventive control method comprises the step of first sensing vehicle operating conditions, such as, for example, vehicle acceleration or clutch temperature. Second, the control unit determines whether the clutch is being operated in a partially engaged state by comparing the sensed operating condition(s) to a predetermined reference value. Third, if it is determined that the clutch is being operated in the partially engaged state, the control unit issues an output signal to the engine controller commanding that the engine speed be repetitively increased and then decreased a predetermined amount. The increase and decrease of the engine speed causes the clutch to further engage and then disengage. The repetitive partial engagement and disengagement of clutch will not cause the vehicle to move, but will cause the vehicle to slightly shake warning the driver that clutch is being operated in a partially engaged state.
Among other advantages, the inventive control system and method of controlling operation of a vehicular transmission system discourages the driver of a vehicle employing a centrifugal master friction clutch from operating the clutch in a partially engaged state for a prolonged period of time. Moreover, the inventive control system and method prevents the clutch from being automatically engaged or disengaged too quickly in the event the clutch is being operated in a partially engaged state.
Various additional aspects and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, when read in light of the accompanying drawings.